1. Field of the Invention
The present invention relates to a vehicle in which respective pairs of front and rear wheels can be driven and which is designed so that a rider may sit astride the vehicle.
2. Description of the Prior Art
There is known a vehicle which is generally travelable on a road such as a rough road, damp road, snowy road, etc., (Japanese Patent Application Laid-open No. 421/83). A vehicle is also well known in which front and rear wheels are mounted respectively in a pair and all the wheels can be driven to enhance the driving performance.
Because the above-described vehicles may travel on a road such as a rough road, damp road, snowy road, etc., it is required to set the gravity center thereof at a lower point and to protect a fuel tank and an exhaust muffler by a durable body frame, and further to prevent the fuel tank from being influenced by the exhaust heat emitted from an exhaust system in a power unit. With such conventional vehicles, however, these requirements could not be necessarily satisfied.
In conventional vehicles, a drive shaft of a power unit carried on the central portion of the body frame is disposed to extend longitudinally of the body frame and has its front and rear ends connected to a front wheel driving system and a rear wheel driving system, respectively. An exhaust pipe leading from the engine of the power unit also extends longitudinally of the body frame. Therefore, it is impossible from the viewpoint of space to locate the drive shaft and the exhaust pipe inside the outermost frame portion of the body edge without any hindrance to the power unit and other parts.